May28,i 9 x7 Influence of Crop, Season, Water on Soil Bacteria 
327 
The number of organisms in these plots is highest in spring and lowest 
in fall, and they show an increase due to the irrigation water used. The 
ammonifying powers are highest in summer and lowest in fall, and the 
water applied increases the ammonifying power and is greatest where 
25 inches are applied. The 37.5 inches, while they are better than none, 
depress the ammonifying powers when compared with 25 inches. 
It was thought likely that this decrease in the nitrifying powers and 
formation of nitric nitrogen in these plots with highest water content 
may be due to a difference in temperature. For this reason temperature 
determinations were made on the soil during September and October 
of one season. The determinations were made to a depth of 4 feet 
with soil thermometers placed in the ground and read twice daily, at 
8 a. m. and 5 p. m. The average results for the season are given in 
Table XXVII, expressed in degrees Fahrenheit. 
Table XXVII .—Average temperature (°F.) of the soil at different depths 
Plot. 
39 
40 
41 
43 
Time. 
Firstfoot. 
Second foot. 
Third foot. 
f 8 a. m. . .. 
54-8 
52.1 
49.9 
15 P* m .,. 
55 -i 
52.3 
49*8 
f8 a. m. 
53-9 
52.6 
47.4 
15 P* m . 
53-9 
52.7 
48.9 
f8 a. m. 
54-3 
53-3 
51.8 
ISP- m. 
54-7 
53 * 1 
5 1 * 7 
f8 a. m. 
56- S 
55*4 
52.8 
15 P* m ... 
56.8 
55*6 
52. 6 
Fourth foot* 
47*2 
48.7 
49. 1 
49.4 
50 - 3 
51- a 
This table shows that the temperature is about 2 degrees higher in the 
nonirrigated soil than in the soil receiving the greatest quantity of water; 
and the difference is about the same even in the fourth foot, which has 
a temperature about 6 degrees lower than the temperature of the 
surface soil. The temperature of the soil is only slightly different in 
morning and evening, but the difference extends to a depth of 4 feet* 
The nitrifying powers are highest in midsummer, at which time they 
are apparently increased by the irrigation water, but are depressed by 
the larger quantities in the fall. 
The results which we have considered indicate that the irrigation 
water applied has clearly depressed the number of organisms which 
develop upon synthetic agar in alfalfa, oats, and potato soil. The re¬ 
sults obtained for the com are not regular, but there is a marked increase 
in the fallow. 
The ammonifying powers were increased in all of the soils except the 
alfalfa, and in this case there was a decrease. 
The nitrifying powers have been increased in every case except in the 
oat soil. The average results for the different water treatments are 
given in Table XXVIII. 
